In order to fill-package a variety of foods and beverages, cosmetics, pharmaceutical products, miscellaneous goods and other articles, plastic flexible packaging bags of various shapes have been developed and put into practical use in the past. As laminated materials (laminates) that are packaging materials for forming the packaging bags, a variety of gas barrier materials having properties to prevent permeation of oxygen gas, water vapor and the like have been used from the viewpoints of protection of qualities of the contents, demand for extension of storage time, etc. However, there is a problem that sunlight from the sun, fluorescent light from a fluorescent lamp, or the like is transmitted, and this transmitted light exerts influence on the contents to cause decomposition of the contents, change of properties thereof or photo deterioration such as discoloration and others. On this account, a variety of light-shielding materials have been also studied and proposed. As the most popular material to impart a gas barrier function or a light-shielding function, a laminated film of an aluminum foil and a resin, an aluminum-deposited film or the like has been used.
Polyolefin-based resins including polypropylene are inexpensive, are excellent in moldability and are excellent also in oil resistance, sealing properties, etc., and therefore, they can exhibit excellent performance also in the case where they are used as such packaging materials as above (e.g., patent literatures 1 and 2). However, the polyolefin-based resins generally have poor adhesion to different materials, and hence, when a laminate of, for example, an inorganic layer of deposited aluminum or the like and such a resin is formed, deposition strength (bond strength) between the polyolefin-based resin layer and the inorganic layer is poor, and depending upon the use environment or the use purpose, an interlaminar peel (delamination) phenomenon sometimes takes place. In order to prevent such delamination, various methods have been proposed, and a part of them have been put into practical use. For example, for the purpose of enhancing adhesion to metals, etc., a method of grafting maleic anhydride or the like on polypropylene through a specific technique has been proposed, or for the purpose of imparting flexibility to polypropylene inherently having a property of rigidity, a method of compounding a soft rubber has been proposed (patent literatures 3 and 4).
On the other hand, in order to allow resin packaging bags for various foods including snacks, particularly inside parts of the bags, to have brightness and gloss, the bags are sometimes required to have metallic appearance (glitter feeling) or pearl-like appearance. Also the aforesaid packaging bags formed of aluminum foils or aluminum-deposited films are no exception, and for example, strong packaging bags hardly suffering delamination and having sufficient glitter feeling on the interior parts have been desired by customers in a specific region or food makers.
Enhancement of delamination prevention performance has become feasible by the aforesaid various proposals including a grafting method and a rubber compounding method, but it is still difficult to allow the packaging bags to simultaneously exhibit glitter feeling, and the need for it by the customers has increased.